// Problem: 
// Contest: 
// URL: 
// Memory Limit: 
// Time Limit: 
// #pragma GCC optimize("Ofast")
// #pragma GCC optimize("unroll-loops")
// #pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,avx2,tune=native")
#include<bits/stdc++.h>
using namespace std;
#define int long long
inline int read(){
	int s=0,w=1;
	char ch=getchar();
	while(ch<'0'||ch>'9'){if(ch=='-')w=-1;ch=getchar();}
	while(ch>='0'&&ch<='9') s=s*10+ch-'0',ch=getchar();
	return s*w;
}
int ans=0;
bool row[201000]={0};
bool col[201000]={0};
bool dig1[201000]={0};
bool dig2[201000]={0};
signed main()
{
	int n,m,k,x,y;
	cin>>n>>m>>k;
	for(int i=1;i<=k;i++)
	{
		cin>>x>>y;
		row[x]=1;
		col[y]=1;
		dig1[x+y]=1;
		dig2[x-y+max(n,m)]=1;
	}
	for(int i=1;i<=n;i++)
	{
		if(row[i]==1)continue;
		for(int j=1;j<=m;j++)
		{
			if(col[j]==1||dig1[i+j]==1||dig2[i-j+max(n,m)]==1)continue;
			ans++;
		}
	}
	cout<<ans;
	return 0;
}
